Magnetic recording medium substrate, method of producing the same, and method of evaluating magnetic recording medium

ABSTRACT

The present invention relates to a substrate for a magnetic recording medium that ensures a floating height on a magnetic head. This substrate is made of a sintered body provided with pores having a diameter in the range of 0.05 μm to 2.0 μm extending across 5% to 50% of the surface area of the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to magnetic recording media usedin magnetic recording and reproducing apparatuses, and, moreparticularly, to a substrate for a magnetic recording medium that canreduce the floating height of the magnetic head in compliance withhigher recording densities. The present invention also relates to amethod of evaluating a magnetic recording medium that can reduce thefloating height of the magnetic head.

2. Description of the Related Art

For a magnetic recording medium, such as a magnetic disk, the substrateis produced by providing nickel-phosphorus plating on the surface of analuminum alloy, for instance, and polishing the resultant. On thesurface of the substrate, irregularities are formed by a textureprocess. The reason why those irregularities are positively formed onthe surface of a magnetic recording medium is that the magnetic head canmagnetically record and reproduce information on the magnetic recordingmedium while maintaining a very small floating height from the magneticrecording medium. In this manner, the magnetic head can be preventedfrom adhering to the surface of the magnetic recording medium, and thefrictional resistance can be reduced.

In recent years, however, there has been an increasing demand forhigher-density magnetic recording and reproduction apparatuses, such asmagnetic disk devices used in computers. In response to such a demand,it is necessary to reduce the magnetic spacing between the magnetic headand the magnetic disk, i.e., the floating height of the magnetic head,as much as possible. Recently, a glide height value that is the distancefrom the disk average surface is required to be 10 nm or less, and ahead floating height is required to be 30 nm or less.

Japanese Laid-Open Patent Application No. 9-326115 discloses a techniqueof reducing the head floating height by evaluating the undulations andripples formed by the irregularities on the surface of a magneticrecording medium.

Also, a magnetic recording medium having a non-texture process performedthereon has been suggested. The non-texture process is performed torestrict the irregularities on the surface within a predetermined rangeso as to reduce the head floating height. However, the non-textureprocess cannot solve the problem of head adhesion.

The technique disclosed in Japanese Laid-Open Patent Application No.9-326115 involves the evaluation of the undulations and ripples in thecircumferential direction (the recording and reproducing direction ofthe magnetic head). In this technique, the floating height of themagnetic head is restricted to 100 nm or smaller. In recent years,however, there has been a demand for magnetic heads having even smallerfloating heights, such as 30 nm or less. As a result, it has becomedifficult to realize such a small floating height only by putting arestriction on the shapes of irregularities in the circumferentialdirection of the magnetic disk.

Furthermore, in the conventional magnetic disk apparatuses, a contactstart stop (CSS) method in which the floating surface of the magnetichead is brought into contact with the surface of a magnetic disk andthen slidably moves on the surface of the magnetic disk is widelyemployed. In order to reduce the floating height, it is necessary toperform the texture process and reduce the heights of the irregularitieson the surface of the magnetic disk. However, if the irregularities onthe surface of the magnetic disk are made too small in height, thesurface of the magnetic disk is smoothed. This will result in theproblems of the adhesion and high friction of the magnetic head at thetime of contact start and stop.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide substrates formagnetic recording media in which the above disadvantages areeliminated.

A more specific object of the present invention is to provide asubstrate for a magnetic recording medium that is formed by apredetermined material so as to reduce the floating height of a magnetichead.

Another specific object of the present invention is to provide a methodof evaluating a magnetic recording medium that can reduce the floatingheight of a magnetic head.

The above objects of the present invention are achieved by a substratefor a magnetic recording medium that comprises a sintered body providedwith pores having a diameter in the range of 0.05 μm to 2.0 μm extendingacross 5% to 50% of the surface area of the substrate.

With this substrate for a magnetic recording medium, the surface of thesubstrate is provided with a large number of pores even if the surfaceappears to be flat. Accordingly, a magnetic recording medium formed bythis substrate has only a small contact area with the magnetic head.Even if the floating height becomes small and the magnetic head isbrought into contact with the surface of the magnetic recording medium,there will be no problem of adhesion and high friction with the magnetichead.

The above objects of the present invention are also achieved by a methodof manufacturing a substrate for a magnetic recording medium, comprisingthe step of sintering a particle material containing a porous materialat a temperature higher than the melting point of the porous material.The particle material may be aluminum particles. The porous material isnot specifically limited, but should preferably be one material selectedfrom the group consisting of lead, copper, magnesium, nickel, zinc, tin,manganese, silicon, glass, and resin.

By this method, when a magnetic layer and a protection layer are formedon the substrate, the floating height of the magnetic head can bereduced, thereby obtaining a magnetic recording medium having a higherrecording density.

The above objects of the present invention are also achieved by a methodof evaluating a magnetic recording medium, comprising the steps of:

measuring the maximum height of each of a plurality of waveforms havingdifferent wavelengths in the moving direction of a magnetic head on thesurface of the magnetic recording medium; and

determining the sum of the maximum heights of the plurality ofwaveforms.

This method further includes the steps of:

measuring the maximum height Wp of undulations having a wavelength of2.5 mm or larger in the recording/reproducing direction of the magnetichead, the maximum height MWp of ripples having a wavelength in the rangeof 10 μm to 2.5 mm, and the maximum height Rp of minute ripples having awavelength of 10 μm or smaller; and

comparing a required glide height value with the sum of Wp, MWp, and Rp,

wherein the maximum height RCmax of irregularities in the scanningdirection of the magnetic head is 20 nm or smaller in the floatingguaranteed area (or the recording area) on the magnetic head.

By the above evaluation method, the glide height value required for amagnetic recording device is determined and then compared with the sumof Wp, MWp, and Rp. In this manner, it is determined whether or not themagnetic recording medium is suitable for high-density recording with asmall floating height.

It should be understood here that the moving direction of the magnetichead is the radial direction of a disk while the recording/reproductiondirection of the magnetic head is the circumferential direction of thedisk. The moving direction and the recording/reproduction direction ofthe magnetic head are perpendicular to each other.

The above and other objects and features of the present invention willbecome more apparent from the following description taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged view of the surface of a magnetic disk in itscircumferential direction;

FIG. 2 shows extracted undulations from the irregularities shown in FIG.1;

FIG. 3 is an enlarged view of a part of the undulations shown in FIG. 2;

FIG. 4 is an enlarged view of a part of the ripples shown in FIG. 3;

FIG. 5 is an enlarged view of the surface of the magnetic disk in itsradial direction;

FIG. 6 shows the data obtained from substrates A to E;

FIG. 7 shows the result data obtained from examples and comparativeexamples with respect to the substrates A, B, C, and E;

FIG. 8 shows the result data obtained from an example and a comparativeexample with respect to the substrate D;

FIGS. 9A and 9B show the process in which a large number of pores areformed on a magnetic recording medium substrate produced in accordancewith a second embodiment of the present invention;

FIG. 10A is a schematic view of the surface of a conventional substratehaving bump protrusions;

FIG. 10B is a schematic view of the surface of the substrate produced inaccordance with the second embodiment of the present invention;

FIG. 11 shows the relationship between the density of pores and thefrictional resistance in a magnetic recording medium produced using thesubstrate of the second embodiment; and

FIG. 12 shows the relationship between a magnetic head and a rotationalmagnetic disk in a magnetic disk apparatus on which a magnetic diskproduced with the substrate of the second embodiment is mounted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of embodiments of the present invention,with reference to the accompanying drawings.

First Embodiment

FIGS. 1 to 5 illustrate the principles of a first embodiment of thepresent invention. This first embodiment is a method of determiningwhether or not each magnetic recording medium is suitable for reducingthe floating height.

FIG. 1 illustrates the surface condition of a magnetic disk 10 in thecircumferential direction. Seen from a distance, the surface of themagnetic disk 10 is flat, but has irregularities 1 in an enlarged view,as shown in FIG. 1. The irregularities 1 are made up of rough ripples 5as indicated by the minute waveforms in FIG. 1.

Conventionally, the floating height of a magnetic head is determinedfrom the surface irregularities 1 and the rough ripples 5 in thecircumferential direction (normally the longitudinal direction of amagnetic head).

However, when the floating height of the magnetic head is 30 nm or less,it is difficult to judge from the evaluation of the surface roughnessonly in the circumferential direction whether or not the floating heightcan be reduced. In view of this, the present inventors made intensivestudies on the irregularities on the entire surface of a magnetic disk,and have found conditions of a magnetic disk that can achieve a floatingheight of 30 nm or less.

FIG. 2 is an enlarged view of undulations 11 extracted from the surfaceirregularities 1 shown in FIG. 1. In FIGS. 1 to 4, the zero position onthe ordinate axis indicates the center line, which is the averageposition determined from the amplitude of each waveform. In this firstembodiment, the maximum height of the undulations 11 from the centerline is indicated by Wp, as shown in FIG. 2. Here, the undulations 11are a waveform having a wavelength of 2.5 mm or larger.

FIG. 3 is an enlarged view of a part of the undulations 11 shown in FIG.2. The waveform of the undulations 11 shown in FIG. 2 contains ripples12 that have the maximum height MWp. In this embodiment, the ripples 12are a waveform having a wavelength of 10 μm to 2.5 mm.

FIG. 4 is an enlarged view of a part of the ripples 12 shown in FIG. 3.When seeing the undulations 11 and the ripples 12 more closely, thereare minute ripples 13 having a waveform of 10 μm or less. The minuteripples 13 are generally referred to as surface roughness. In thisembodiment, the maximum height of the roughness is indicated by Rp.

As described above, in this embodiment, the surface irregularities areevaluated based on the three waveform elements, i.e., the undulations,ripples, and roughness, in the circumferential direction.

In this embodiment, the undulations in the radial direction of amagnetic disk are also taken into consideration. More specifically, theundulations in the radial direction are evaluated as to whether or notthe maximum height RCmax of the undulations is smaller than apredetermined value.

FIG. 5 shows an enlarged view of the surface condition of a magneticdisk in its radial direction. Due to the chamfering process, aring-shaped protrusion 20 is formed on the outer periphery of themagnetic disk. Accordingly, the maximum height of the protrusion 20 isequivalent to the maximum height RCmax.

The enlarged view in FIG. 5 shows an end portion that is located at adistance of 45.0 mm to 46.6 mm in the radial direction of the magneticdisk, which has a diameter of approximately 95 mm.

A floating guaranteed area (or the recording area) on a magnetic disk isan area in which the floating of a magnetic head is guaranteed. Themagnetic disk concentrically includes a clamp region to be fixed to arotational drive axis (spindle), a CSS region, a data region, and theperipheral region, in that order starting from the center. The floatingguaranteed area of this embodiment is an area that includes the CSSregion, the data region, and a part of the peripheral region.

If the wavelength of the undulations in the radial direction of thesubstrate of a magnetic disk is larger than the length corresponding tothe external shape of the magnetic head in the width direction, afloating loss of the magnetic head is caused. Within the floatingguaranteed area, the maximum height RCmax should be 20 nm or less, andmore preferably, should be 10 nm or less. With such small surfaceirregularities, the floating loss of the magnetic head can be reduced.

The wavelength of the undulations in the circumferential direction ofthe substrate of the magnetic disk also has an influence on the floatingloss of the magnetic head. The wavelength of the undulations in thelongitudinal direction of the magnetic head is preferably three times aslarge as the length corresponding to the external shape of the magnetichead in the longitudinal direction. Furthermore, the wavelength shouldpreferably be in the range of several tens of nanometers to severalmillimeters. If the external shape of the magnetic head in thelongitudinal direction is 2 mm, for instance, the wavelength isapproximately 6 mm.

The wavelength range is divided into three waveform elements, which arethe undulations, ripples, and minute ripples. A waveform having awavelength of 2.5 mm or larger that may be approximately three times aslarge as the length of the magnetic head in the longitudinal directionrepresents undulations. The maximum height of this wavelength isindicated by Wp. A waveform having a wavelength in a range of 10 μm to2.5 mm represents ripples. The maximum height of the waveform isindicated by MWp. A waveform having a wavelength in a range of 50 nm to10 μm represents minute ripples. The maximum height of the minuteripples is indicated by Rp.

Since the simple sum of those maximum heights, which is Wp+MWp+Rp, isequivalent to a required glide height value of the magnetic disk, thesimple sum of the maximum heights is compared with the required glideheight value. More specifically, from the expression, Wp+MSp+Rp≦requiredglide height, it is determined whether or not the magnetic recordingmedium has the required glide height value.

If the magnetic recording medium is the CSS type, the minute ripplesshould preferably have an average roughness Ra of 0.2 nm or larger,because it is necessary to prevent adhesion and to reduce the friction.

To produce a magnetic recording medium that satisfies the smallerfloating height conditions through the above-described evaluationmethod, the polishing pad, the polishing agent, and the processing timeneed to be adjusted as necessary. By doing so, RCmax can be restrictedto 20 nm or less in the radial direction of the magnetic disk, and WP,MSp, and Rp determined from the above expression are realized in thecircumferential direction. The surface roughness can be controlled bythe texture process performed on the substrate prepared formanufacturing the magnetic recording medium.

Next, the manufacturing of the above-described magnetic disk determinedto be suitable for reducing the floating height will be described. Asfor the material for forming the substrate for the magnetic recordingmedium, materials that have conventionally been used for substrates canbe used. Such materials include non-magnetic materials, such as aluminumalloys, glass materials including tempered glass and crystallized glass,resin, and composite materials.

In this embodiment, the substrate is made of aluminum. A rolled platemade of an aluminum alloy is first stamped out into a disk-like platehaving a diameter of 3.5 inches, thereby obtaining a substrate disk. Thesubstrate disk is then subjected to pressure annealing, and a cuttingprocess is performed on the inner and outer diameters by an NC lathe,thereby adjusting the size. Further, both surfaces of the substrate diskare ground with a grindstone having a roughness of No. 2000 to No. 6000,so that both the maximum height Wp of the undulations and the maximumheight MWp of the ripples have desired values. Both surfaces of thesubstrate disk are then provided with a Ni—P plating layer having athickness in a range of 5 μm to 10 μm.

Next, a polishing process is performed to polish both surfaces of theNi—P plating layer. This polishing process is carried out using a 2-sidepolishing machine. As for the polishing solution to be used here, asolution containing oxidizing ions or a solution mainly containingaluminum oxide or silica can be employed. For those solutions, apolishing agent containing alumina can increase the polishing speed andreduce most effectively the maximum height Wp of the undulations and themaximum height MWp of the ripples. Especially, a polishing agentcontaining hexagonal plate-like alumina or calcined alumina is mostpreferable. The hardness of the polishing pad should preferably be inthe range of 60 to 100 in accordance with the JIS A (JIS K-6301)standards. If the polishing pad has a hardness smaller than the aboverange, the outer periphery of the substrate will be too easily polished.As a result, the wavelength of the undulations in the radial directionof the substrate becomes larger than the length corresponding to theexternal shape of the magnetic head in its width direction. The size ofthe polishing agent and the polishing time divided into a few stages aresuitably selected, so that a substrate having the maximum heights Wp,MWp, and Rp can be produced.

In the above manufacturing experiment, substrates A to E were obtained.FIG. 6 shows the data of the substrates A to E.

A texture process described below was performed on the substrates A toE, and a Cr surface treatment film, a CrCoPt magnetic layer, and acarbon-based protection film were formed on the surface of eachsubstrate in that order. After that, a fluorine-based lubricant wasapplied onto the protection film, thereby completing a magnetic disk.

The texture process was carried out by pressing processing tape to arotating substrate while dripping a polishing liquid onto the rotatingsubstrate. The polishing liquid contained polycrystal diamond, and twotypes were employed in the texture process. One of the two types of thepolycrystal diamond had a primary average grain size of 0.15 μm, whilethe other had a primary average grain size of 0.30 μm. As for the otherprocessing conditions, the tape feeding speed was 30 mm/min, the rollpressure was 1 kg, the substrate rotation speed was 450 rpm, theoscillation amplitude was 3 mm, the frequency was 7 Hz, and theprocessing time was 25 seconds.

For the substrates A and B, the texture process was performed under thetwo conditions that the primary average grain sizes of the polishingliquid were 0.15 μm and 0.30 μm. For the substrates C and E, the textureprocess was performed, with the primary average grain size being 0.30μm. For the substrate D, the texture process was performed, with theprimary average grain size being 0.15 μm. At the same time, anexperiment was conducted by performing no texture process on thesubstrate D for a comparison purpose.

A magnetic recording medium was formed under the above textureprocessing conditions. The glide height value, the maximum heights Wp,MWp, Rp, and RCmax, the average roughness Ra, and the frictionalcharacteristics were measured.

The maximum heights Wp and MWp in the circumferential direction of themagnetic recording medium, and the maximum height RCmax of theundulations in the radial direction were measured using an opticalinterferometer. In the measurement of MWp and RCmax, in which themeasurement range was narrow, the field of view was 2.5 mm×1.8 mm. Themeasurement range of RCmax was 45.0 mm to 46.6 mm in the radialdirection.

The roughness Ra was measured by an AFM, and the measurement range was10 μm×10 μm.

The measurement of the glide height value was carried out using amagnetic head having a length of 2.0 mm in the longitudinal direction(i.e., the circumferential direction of the magnetic recording medium).The floating characteristics of the magnetic head had been alreadychecked in advance. A contact between the magnetic disk and the magnetichead was then detected by a piezosensor. Based on the rotation speed ofthe magnetic disk at the time of the contact, the glide height value wasdetermined as the highest point on the magnetic disk. The measurementlocation of the glide height was at the center of the magnetic head, ata radial location R of 30.0 mm from the center of the magnetic disk, andat a radial location R of 45.8 mm from the periphery of the magneticdisk.

FIG. 7 shows the results of experiments and comparative experimentsconducted on the substrates A, B, C, and E. When the sum of Wp+MWp+Rpwas 10 nm or smaller (in Examples 1—1 to 1-4), the glide height at thecenter of the magnetic head and the radial location R of 30.00 mm was 10nm or smaller, as shown in FIG. 7.

When the maximum height RCmax was 20 nm or larger, the glide heightvalue exceeded 10 nm at the radial location R of 45.8 mm on theperipheral side, even if the sum of Wp+MWp+Rp was 10 nm or smaller andthe glide height at the radial location R of 30 mm was 10 nm or smaller.As a result, the surface shapes could not satisfy the conditions(Comparative Example 1—1).

FIG. 8 shows the data obtained from the substrate D. In ComparativeExample 2, the sum of Wp+MWp+Rp was 10 nm or smaller, and the glideheight was 10 nm or smaller. However, no texture process was performed,which resulted in insufficient surface roughness. As a result, theinitial frictional coefficient was 5 or larger. With such a high initialfrictional coefficient, there will be great possibilities of adhesion ofthe magnetic head and excessive frictional resistance, when used in aCSS-type magnetic recording apparatus.

In Example 2, on the other hand, the average roughness Ra of thesubstrate after the texture process was 0.20 nm or larger, so that theinitial friction coefficient was 2.0, which is much lower than 5. Withsuch a low initial friction coefficient, there will be no such problemsas adhesion of the magnetic head and frictional resistance.

By the above method of evaluating magnetic recording media, it becomespossible to detect magnetic recording media that can ensure smallfloating heights.

Second Embodiment

A second embodiment of the present invention involves the material ofthe substrate, which is formed so as to ensure a small floating heightof the magnetic head. More specifically, when a substrate for a magneticdisk is formed, a large number of pores are formed on the surface of thesubstrate so as to reduce the contact area with a magnetic head. Such asubstrate for a magnetic recording medium can ensure a small floatingheight of the magnetic head.

The substrate for a magnetic recording medium of this embodiment isformed as a sintered body that is provided with pores having a diameterof 0.05 μm to 2.0 μm extending across 5% to 50% of the surface area. Amagnetic recording medium manufactured from this substrate has only asmall contact area, even when the floating height of the magnetic headis reduced. Accordingly, there will be no trouble caused by adhesion ofthe magnetic head or a high frictional resistance.

In the following, the second embodiment will be described in greaterdetail, with reference to FIGS. 9A and 9B through 12. FIGS. 9A and 9Bshow the step of forming a large number of pores on a magnetic recordingmedium substrate 50.

Conventionally, an aluminum material or a glass material having ametallic material formed on the surface has been generally used as thematerial for a substrate for a magnetic recording medium. In thisembodiment, however, a particle material that can be sintered is used.Examples of such a particle material includes aluminum particles. Forinstance, a base member is formed by mixing the aluminum particles withlead stearate as a lubricant for preventing burning. A material forforcibly forming pores (this material will be hereinafter referred to asthe “pore-forming material”) is then applied to the base member.

The pore-forming material is not strictly defined, but can be anymaterial, as long as it has a large number of pores on the surface afterthe aluminum particles are sintered to form the substrate (in adisk-like form). The pores are formed as a result of melting,evaporating, or sublimating at a temperature lower than the sinteringtemperature. The pore-forming material can be selected from the groupconsisting of lead, copper, magnesium, nickel, zinc, tin, manganese,silicon, glass, and resin such as vinyl chloride.

In a case where lead is used as the pore-forming material, leadparticles having a diameter of 0.1 μm to 2.0 μm are blended on the basemember at a proportion of 5% to 50% with respect to the surface area ofthe substrate, thereby obtaining a substrate material prior to thesintering.

In the step of FIG. 9A, after the aluminum particles 51 are compressedinto a predetermined shape by a pressing device, lead particles 55 arescattered on the compressed aluminum particles 51.

The step of FIG. 9B shows the substrate 50 after aluminum sintering at atemperature slightly lower than 600° C. The melting point of lead isapproximately 330° C. Therefore, the lead particles 55 melt at thetemperature of almost 600° C., and flow into pores 52 formed in thesintered aluminum particles 51. As a result, new pores 56 appear atlocations where the lead particles 55 existed prior to the melting.

The second embodiment involves the porous characteristics of acompressed molding material. The diameter and density of the pores varywith the size of particles used for sintering and the sinteringtemperature. The sintered body obtained by sintering the aluminumparticles 51 is a porous material having a large number of pores. Themelted lead flows into the pores so that the new pores 56 are formed atthe location where the lead particles 55 used to exist. The pores 52formed in the compressed aluminum particles 51 reduce the contact area.However, to control the diameter and the density of the pores, the newpores 56 are forcibly formed by adding the pore-forming material.

In this embodiment, the lead particles 55 melt at a sinteringtemperature, and then are absorbed into the compressed aluminumparticles 51, thereby forming the new pores 56. However, the formationof new pores is not limited to this, as long as the porous materialvanishes from its original locations after a sintering process.Accordingly, it is also possible to form new pores by evaporating orsublimating the porous material by the aluminum sintering process. Thestate of the pores formed on the surface of the sintered body can becontrolled by changing the size and the amount of the pore-formingmaterial.

The magnetic recording medium substrate formed in the above-describedmanner can be used as it is. However, in order to improve theperformance of the sintered body, it is possible to performre-compressing of the substrate and re-sintering of the re-compressedsubstrate.

Furthermore, a polishing process may be performed so as to increase thesmoothness of the surface of the substrate. By the polishing process,the surface of the substrate may be in a non-texture state, having anaverage roughness Ra of only 0.1 nm. Considering the fact that theaverage roughness Ra of a conventional magnetic recording medium is inthe range of 0.4 nm to 0.6 nm, and that the maximum roughness of such aconventional magnetic recording medium is in the range of 6 nm to 7 nm,the average roughness Ra of 0.1 nm represents an extremely smoothsurface.

The substrate of this embodiment, however, has a large number of pores56 on its surface. Accordingly, there will be no problems such asadhesion of a magnetic head, and the glide height of a magnetic head canbe restricted to a small value. Thus, a magnetic recording medium formedfrom the substrate of this embodiment can ensure a small floating heightof a magnetic head.

FIGS. 10A and 10B illustrate the features of the magnetic recordingmedium substrate formed in accordance with the second embodiment of thepresent invention. FIG. 10A schematically shows the surface of aconventional substrate having bumps. FIG. 10B schematically shows thesurface of the substrate formed in accordance with the second embodimentof the present invention.

As shown in FIG. 10A, a plurality of rectangular wave protrusionscorresponding to the roughness stand from the flat face 60 of thesurface of the substrate, but the heights of the rectangular waveprotrusions are not uniform. Especially, the height of the region of apump 62 represents the maximum height 63. A glide height value issubstantially determined by the maximum height 63. Such bump protrusionsare employed to prevent the adhesion of a magnetic head. Because ofthis, it is difficult to restrict the glide height value to a smallvalue, as already mentioned.

It should be understood here that a dot and dash line 65 shown in FIG.10A represents the center line as the average roughness.

Meanwhile, in the case of the substrate of the second embodiment shownin FIG. 10B, the highest ends of the surface of the substrate constitutea flat face 70. There still remain a plurality of rectangular waveprotrusions corresponding to the roughness. However, those rectangularwave protrusions are located below the flat face 70 and do not restrictthe floating height of a magnetic head. In this case, a glide height maybe indicated by the distance 73 between the center line 75 and the flatface 70.

FIG. 11 illustrates the relationship between the density of the poresand the frictional resistance in a magnetic recording medium formed withthe substrate of this embodiment. As is apparent from this figure, thefrictional resistance can be lowered by forming the pores across 5% to50% of the surface of the substrate, preferably, 10% to 40% of thesurface of the substrate, or, more preferably 20% to 30% of the surfaceof the substrate. To measure the density of such pores, the number ofpores in a region of 100 μm×100 μm determined with an opticalmicroscope, for instance, should be counted.

The porous region may occupy the entire surface of the substrate. In acase of a CSS-type magnetic recording medium, it is also possible tosinter a substrate in such a manner as to form the pores in the CSSregion. In other words, a predetermined amount of porous material may beblended in the CSS region prior to the sintering process.

For the substrate of this embodiment, a magnetic layer and a protectivelayer are formed on the substrate using a sputtering apparatus, forinstance, thereby obtaining a magnetic recording medium such as amagnetic disk. In such a case, a Ni—P plating process or a textureprocess can be performed on the substrate, if necessary, prior to theformation of the magnetic layer.

The following is a description of a case where a magnetic disk formedfrom the substrate of the second embodiment of the present invention ismounted on a magnetic recording/reproducing apparatus.

FIG. 12 shows the relationship between a magnetic head 120 and arotating magnetic disk 110 in a magnetic disk apparatus 100. Themagnetic disk 110 is formed by laminating an underlayer 113 and amagnetic film 115 on a substrate 111 formed in accordance with thesecond embodiment of the present invention. A protection film 117containing amorphous carbon is formed on the magnetic film 115, and afluorine-based lubricant film 119 is further formed on the protectionfilm 117. The detailed view of the surface of the substrate 111 is notshown in FIG. 12.

A CSS region in which the magnetic head 120 is brought into contact withand slidably moves on the surface of the magnetic disk 110 at the timeof rotation start or stop of the magnetic disk 110 is formed in themagnetic disk apparatus 100.

The magnetic disk apparatus 100 can ensure a smaller glide height and asmaller floating height for the magnetic recording medium 120, comparedwith the prior art. Furthermore, there will be no problems such asadhesion of the magnetic head 120 in the CSS region.

The present invention is not limited to the specifically disclosedembodiments, but variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority application No.2000-159101, filed on May 29, 2000, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A method of manufacturing a substrate of aluminum for a magnetic recording medium, comprising the step of: sintering a particle material of aluminum containing a pore-forming material at a temperature higher than the melting point of the pore-forming material to form a magnetic recording medium.
 2. The method as claimed in claim 1, wherein the pore-forming material is at least one material selected from the group consisting of lead, magnesium, zinc, tin, a glass, and a resin.
 3. A method of manufacturing a substrate for a magnetic recording medium, comprising the step of: sintering metal particles together with a pore-forming material at a temperature higher than the melting point of the pore-forming material to form the magnetic recording medium. 